Phase comparison radio navigation system with time-sequenced transmissions from spaced stations using selectable phase memory oscillators in a receiver

DETAILED DESCRIPTION According to the present invention, in a receiver for a phase comparison radio navigation system of the kind in which spaced transmitting stations radiate phase-locked signals in a time-shared sequence and in which the receiver has oscillators each phase-locked to a received signal to provide a phase memory enabling comparison signals of the same frequency to be simultaneously available for phase comparison, there are provided two or more display units, each display unit including a digital phase comparator including a counter and decimal digital display for indicating the phase relationship between two signals of the same frequency at two inputs to the phase comparator and selector means for connecting the two inputs to each of the phase comparator units to the outputs of any of said oscillators locked to signals of a common frequency.
This arrangement finds particular application in a time-shared system having three or more transmitting stations.
Only two displays are necessary to obtain a fix and conveniently a maximum of three displays would be provided as this would provide in general as much information as can be used at any one time.
In systems having more than four transmitting stations, the provision of the selector means enables selection of appropriate stations.
The importance of this rapidly increases with increase in the number of transmitting stations.
With three transmitting stations, only three base lines are possible.
With four stations, six base lines can be selected.
With five stations, a selection can be made of ten base lines whilst with six stations, there are fifteen possible base lines.
The arrangement however has further particular advantages for sea-borne navigation receivers in that it is no longer necessary to compare the phase of signals from two or more secondary or slave stations each with a signal from a prime or master station.
It is possible to compare the phase of signals from two secondary stations.
More generally one can select a base line between any pair of stations and this, particularly in survey work or where very accurate positional information is required, enables selection to be made for example of a base line between two secondary stations with land obstructions between them by locking both these stations to a suitably situated prime station